This Application claims priority to Taiwan Patent Application No. 092103685 filed on Feb. 21, 2003.
The present invention relates to a data driver for an active matrix organic light emitting display (AMOLED), which is configured to convert digital voltage signals into analog current signals to drive pixels in the display to emit light.
Pixels in an AMOLED are driven by analog current signals; however, the signals that control the pixels to emit light are digital voltage signals. Therefore, each AMOLED needs a data driver (or source driver) to convert digital control voltage signals into analog current signals.
FIG. 1 illustrates a data driver 1 of the prior art. As it shows, the data driver 1 includes a first shift register 101, a data register 103, a voltage latch 105, a converter 107, a current latch 109, a current source 111, and a second shift register 113. The converter 107 is configured to receive the digital voltage signals 110, which will later drive pixels to emit light, from the voltage latch 105, and to convert the digital voltage signals 110 into analog current signals 112 based on the reference currents provided by the current source 111. The second shift register 113 is configured to switch on or off each cell in the current latch 109 in order to store the analog current signals 112 sent by the converter 107. After a proper period of time, an enabling signal 108 enables the current latch 109 so that all the analog current signals 114, identical to the analog current signals 112, are able to reach all pixels of the AMOLED to present a transient frame.
The framework of the converter 107 is basically a current mirror. FIG. 2 illustrates one kind of current mirror of the prior art. With reference to FIG. 2, a reference current Is, generated by the current source 111 shown in FIG. 1, mirrors Ip1, Ip2, Ip3, etc. through a transistor MP1. It is noted that the values of the mirrored currents, e.g. Ip1, Ip2, Ip3, etc., are associated with the characteristics, i.e. aspect ratio, threshold voltage, and mobility, of MP2, MP3, MP4, etc. Once any deviation from the theoretical characteristics of the transistors is induced during fabricating, the practical values of the mirrored current Ip1, Ip2, Ip3 etc. will bring error as well. The error, even if it is tiny, might still influence the gray level that an analog current signal actually sets in due to the narrow band of each gray level and, therefore, pixels might emit unexpected illumination.
The present invention discloses a data driver for an active matrix organic light emitting display (AMOLED), which converts digital voltage signals into analog current signals in order to drive all pixels in the display to emit light.
The data driver includes a first shift register, a data register, a data latch, a second shift register, and N converters The first shift register is configured to provide an N-bit first control signal The data register is configured to store N M-bit digital voltage signals by switching on the cells in it in turn in response to the first control signal, and to send the N digital voltage signals to the data latch. The data latch is configured to receive the N digital voltage signals and respectively transmit them to the N converters in response to an enabling signal. The second shift register is configured to provide an (M+1)-bit second control signal to control the procedure of converting the digital voltage signals into analog current signals.
Each converter of the data driver of the present invention is a digital-voltage-to-analog-current converter with M units regarded as current sources. Each current source (or each unit) includes two control signals to enable or disable the transistors within so as to control the generation timing of mirrored currents. The current source can overcome the drawbacks of the prior art and, therefore, the mirrored current does not deviate even if the characteristics of the transistors within have been changed during fabricating.